The challenges of identifying Particle-Accelerating Colliding-Wind Binaries

Massive stars are frequently found in binary or higher-multiplicity systems. In such configurations, their strong stellar winds are likely to collide, generating high Mach number shocks. More than 50 of these systems have been identified as particle accelerators, likely through Diffusive Shock Acceleration in the colliding-wind region. While a few have been detected via their high-energy emissions, the primary evidence for relativistic particles comes from synchrotron radio emission. Radio observations, therefore, play a crucial role in identifying particle accelerators and potential targets for high-energy studies. However, various physical factors introduce significant biases, making it challenging to detect clear evidence of particle acceleration. This contribution aims to review the key challenges in this framework, incorporating recent insights motivated by new observational findings.